For some time, the Applicant has produced a wrist for an industrial robot having:
a first body which is intended to be carried by the distal end of a robot arm which has a longitudinal axis, PA0 a second body which is rotatable on the first body about a second axis which intersects the longitudinal axis of the robot arm at right angles, PA0 a third body which is rotatable on the second body about a third axis which intersects the second axis at right angles, PA0 first and second electric motors for rotating the second and third bodies respectively, and PA0 first and second "Harmonic Drive" reduction units which are interposed in the connection between the first motor and the second body and in the connection between the second motor and the third body, respectively, PA0 each reduction unit including: PA0 a) the first electric motor is mounted on the first body, PA0 b) the second electric motor is mounted on the second body, and PA0 in each of the two reduction units, the structure which supports the output rotor of the reduction unit for rotation is constituted by the load-bearing element which forms part of the reduction unit.
a load-bearing element which is fixed to the first body or the second body, respectively, PA1 an input rotor which is supported for rotation on the load-bearing element by a rolling bearing, and PA1 an output rotor which is coaxial with the input rotor and is supported for rotation by a rolling bearing on a structure fixed to the load-bearing element.
In the aforementioned robot, which was previously produced by the Applicant, both of the motors for driving the wrist were carried by the structure of the robot arm and were connected to the two rotary bodies of the wrist by means of mechanical transmissions so that the activation of only one of the motors not only rotated the respective rotary body but also affected the rotation of the other rotary body of the wrist. In order to rotate the second body or the third body alone, it was therefore necessary to operate both of the motors according to a predetermined criterion. Another disadvantage of the known solution consists of the fact that the structure which supported the output rotor of each reduction unit for rotation did not form part of the reduction unit but was a part of the robot wrist. Consequently, when the wrist was assembled, a rolling bearing had to be provided between the support structure and the output rotor of the reduction unit. Assembly was therefore quite laborious and lengthy.